1. Field of the Invention
The present invention relates to a block-shaped measuring chamber unit defining one or more interconnected depressions. Such unit may, for example, be used in electrochemical measuring devices in which case measuring instruments may be sealed to the unit for closing the depressions so as to form measuring chambers.
2. Description of the Prior Art
Electrochemical measuring devices or apparatuses of the type adapted to make a number of different measurements simultaneously or successively in a corresponding number of communicating measuring chambers defined in a measuring chamber unit, are known. In cases where the measuring apparatus or device should be able to make very accurate measurements on a very small liquid or fluid sample, heavy demands must be made on the measuring chambers and the interconnecting passages. Whether the fluid sample on which the measurements should be made is in the form of gas or liquid (which possibly contains dissolved gas) the inner surfaces defining the measuring chambers and the interconnecting passages must be of such a nature that they do not change the composition or characteristics of the fluid sample to any substantial degree when the sample is passed through the measuring chamber unit. Such a change of the composition of the fluid sample may for example be caused by contamination with substances retained in the measuring chambers under a preceding measuring procedure, by absorption of gas from the walls of the measuring chambers into the fluid sample, or by absorption of gas given off from the fluid sample and absorbed by the walls of the measuring chambers. For the reasons stated above it is desirable to make measuring chamber units of the type in question from a material having a high surface density and being inert to the fluid sample, for example stainless steel or glass. However, when these materials are used it is necessary to finish the surfaces of the measuring chambers and the connecting passages by grinding or polishing. Normally, the measuring chambers as well as the interconnecting passages have very small dimensions and are of relatively complex shapes, and therefore, the production of such a measuring chamber unit from glass, stainless steel, or a similar material is relatively expensive. In order to reduce costs it has often been found necessary to make the measuring chamber unit from plastic even though that material is less suitable and in some cases changes the composition of a fluid sample introduced into the measuring chamber unit to such an extent that the error of measurement introduced must be compensated for, if possible.
U.S. Pat. No. 3,997,420 discloses a measuring chamber unit having measuring chambers defined by a number of mutually spaced depressions formed in the same flat surface of a block-shaped body, and adjacent depressions are interconnected by means of V-shaped connecting passages. Such V-shaped passages are disadvantageous because residues of a sample on which measurement is made, is liable to deposit at the bottom of the "V". Furthermore, the V-shaped passages are extremely difficult to clean between successive measurements so that a sample of which measurements are to be made may be contaminated by residues of a preceding sample. U.S. Pat. No. 3,661,010 discloses an analyzing apparatus in which oppositely directed measuring instruments are arranged at opposite ends of a single through-going, cylindrical measuring chamber provided with inlet and outlet passages extending at right angles to the axis of the cylindrical measuring chamber. This known principle may only be used for an equal number of measuring chambers, and in order to obtain a desired small volume of each measuring chamber the spacing between the oppositely arranged measuring instruments must be relatively small. Furthermore, the shape of the measuring chamber is to a high extent determined by the shapes of the oppositely arranged active surface parts of the measuring instruments. These facts severely limit the freedom of choice of a designer constructing an analyzing apparatus including the measuring chamber unit.